1. Field of the Invention
This invention pertains in general to tape cartridges adapted for the magnetic recording of information and in particular to an improved cartridge having increased tape capacity and higher performance.
2. Description of the Related Art
For many years, magnetic recording tape has been utilized as an inexpensive and reliable medium for the storage and retrieval of data processing information. In the personal computer industry, it has become the practice to use tape cartridges to hold the tape and facilitate easy loading of the magnetic tape into a suitably adapted tape drive. Moreover, cartridges protect the magnetic recording tape from contamination and inadvertent contact during operation within the tape drive, as well as during storage outside of the tape drive. Wide acceptance of tape cartridges promoted adoption of standard configurations by the data processing industry.
As the data processing industry advances, there is a need for larger-capacity, belt-driven tape cartridges. Such larger tape cartridges may have a cartridge-drive interface compatible with commercially available industry standard tape drives. If the cartridge is not compatible with industry standard tape drives, the cartridge should have a mechanism to prevent the cartridge from being inserted into an incompatible tape drive.
One way to increase the capacity of a tape cartridge is to increase the length of tape stored therein. Since the volume within a tape cartridge is limited, some cartridge designs increase tape length by decreasing the thickness of the tape. Other designs increase available volume by extending the length of the cartridge while maintaining an industry standard cartridge-drive interface (see, for example, U.S. Pat. No. 4,262,860).
However, lengthening the tape exacerbates undesirable characteristics in the cartridge design. For example, tape tension is attributable to the difference in belt tensions applied to the two tape packs. This is a function of the diameters of the two packs and changes as tape moves from one pack to the other. A bow-tie tension profile of tape moving within a conventional belt-driven tape cartridge indicates the change in tape tension over the entire length of tape as it moves from hub to hub within the cartridge. The bow-tie profile is partly determined by the ratio of the diameter of an empty hub to the diameter of a full tape pack on a hub. Since a longer tape results in an increased tape pack diameter, a longer tape worsens the bow-tie profile of tape tension for a given design of tape cartridge.
Similarly, the tangential drive force (xe2x80x9cTDFxe2x80x9d) is the amount of force needed to drive the tape within a cartridge in either direction. TDF is determined by the total drag of all components in the cartridge and is preferably constant regardless of the amount of tape on each pack. The drags produced by certain components, like the rollers guiding the drive belt, however, vary as a function of the tape pack diameter. As with the bow-tie tension profile, therefore, a longer tape results in a greater variation in TDF as the tape moves from pack to pack. These variations in the bow-tie tension and TDF profiles may detract from the performance of the tape cartridge.
In addition, the tape in the tape packs tends to vertically shift when the tape cartridge is subject to stress. To limit the extent of this shift, some tape cartridges have flanges attached to the top and bottom of each hub. However, these flanges cannot withstand high levels of stress and are not adequate for large tape packs.
Industry standard tape cartridges, moreover, have a door pivotally mounted at the front of the cartridge to protect the tape media passing through an opening in the front face of the cartridge housing when the cartridge is outside of a tape drive. The door is typically biased closed when the cartridge is outside the drive, and cammed open by a rail in the tape drive when the cartridge is inserted therein. The door, however, does not cover a second opening in the front face through which the drive roller and portion of the tape are exposed, and which allows dust and other contaminates to contact the media.
Industry standard tape cartridges additionally have a write protect lock located near the front left comer of the cartridge. This lock is typically a sliding or rotating two-position switch and is often difficult to manipulate.
Accordingly, there is a need for an increased capacity cartridge having a mechanism for preventing insertion into a non-compatible drive and decreased variation in tape tension and TDF commonly associated with cartridges having increased tape length. In addition, the cartridge should have improved hubs to support the larger tape packs, a door that more efficiently protects the media from contamination, and a write protect lock that is easier to manipulate.
In accordance with the present invention, a tape cartridge preferably has a longer housing than industry standard tape cartridges. The cartridge housing has a planar front face having media and capstan access openings compatible with an industry standard tape drive. Preferably, the top and sides of the cartridge include transitional segments positioned rearwardly of the front face which extend laterally outward from the center to make the rear portion of the cartridge wider than the front portion. These transitional segments encounter components of a conventional tape drive that is equipped to receive conventional tape cartridges, and prevent the tape cartridge of the present invention from being fully inserted into such a non-compatible tape drive.
Two tape hubs are rotatably mounted on a baseplate at respective first and second axes of rotation perpendicular to the plane of the front face and slightly askew of a center line extending from the front face of the cartridge to the back of the cartridge. In order to reduce the variation in bow-tie and TDF tension profiles introduced by a long length of tape, the hubs preferably have a larger diameter than the diameter of hubs typically found in other industry-standard tape cartridges. Thus, the ratio of hub size (i.e. empty tape pack) to full tape pack size is reduced, contributing to decreased variations in the bow-tie tension profile. Moreover, each hub preferably has an integrally molded bottom flange and a ultrasonically welded top flange for preventing the tape packs from shifting. In a preferred embodiment, a spring is positioned between the hubs and the housing to bias the hubs toward the baseplate, thereby stabilizing the position of the hubs with respect to the baseplate.
First and second sets of rollers are rotatably mounted on the baseplate in the same plane as the tape hubs and serve to guide a drive belt through the cartridge. Each tape hub has an associated set of three rollers. Two rollers of each of the first and second roller sets are mounted substantially symmetrically with the respective first and second rotational axes of the tape hubs. This arrangement keeps the belt length almost constant regardless of tape pack size, resulting in an almost constant static installed belt tension and a more constant component drag over the full range of tape packs on each hub. A roller in the first set of rollers is the drive roller and has a flange that protrudes through the capstan access in the front face of the cartridge for engaging a capstan of a tape drive when the cartridge is inserted therein. The capstan imparts rotational movement to the drive roller and the associated drive belt which, in turn, rotates the tape packs and moves the tape from pack to pack within the cartridge.
The belt rollers preferably have a constant low level of rotational drag. However, several of the rollers engage segments of the drive belt that are also wrapped around a tape pack. Since the sizes of the tape packs vary as the tape moves through the cartridge, the wrap angles of the belt relative to the low-drag rollers vary. Therefore, the side loads exerted by the belt also vary depending upon tape pack size. Since side load affects the amount of drag produced by a roller, the combined drags of the relatively low-drag rollers vary as a function of tape pack size.
In accordance with one embodiment of the present invention, a high-drag roller associated with the second tape pack is positioned between two low-drag belt rollers and engages the drive belt at a constant wrap angle. Accordingly, the side load exerted by the belt on the high-drag roller is constant and, therefore, the drag produced by the roller is substantially constant. Since the varying drags introduced by the low-drag belt rollers are outweighed by the constant drag introduced by the high-drag roller, the cartridge tends to have a more constant bow-tie tension profile and resulting TDF.
A door is pivotally mounted near the front right corner of the tape cartridge and biased to cover the media and capstan access openings in the front face of the cartridge when the cartridge is outside of the tape drive. In addition, a write protect lock comprising a pivotally mounted arm is positioned near the left front corner of the tape cartridge to selectively engage a sensor switch within a compatible tape drive when the tape cartridge is fully inserted therein.